Integrated circuits often contain voltage reference circuits to provide a stable reference voltage for use with internal circuit operations. The voltage reference circuit is key in many integrated circuits (ICs) and memories where it is vital to have a stable reference voltage for use in many other circuits of the IC or memory. One such commonly used voltage reference is the band-gap voltage reference circuit.
Memory devices are typically provided as internal storage areas in the computer. The term memory identifies data storage that comes in the form of integrated circuit chips. There are several different types of memory used in modern electronics, one common type is RAM (random-access memory). RAM is characteristically found in use as main memory in a computer environment. RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
Computers almost always contain a small amount of read-only memory (ROM) that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. An EEPROM (electrically erasable programmable read-only memory) is a special type non-volatile ROM that can be erased by exposing it to an electrical charge. EEPROM comprise a large number of memory cells having electrically isolated gates (floating gates). Data is stored in the memory cells in the form of charge on the floating gates. Charge is transported to or removed from the floating gates by specialized programming and erase operations, respectively.
Yet another type of non-volatile memory is a Flash memory. A Flash memory is a type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. A typical Flash memory comprises a memory array, which includes a large number of memory cells. Each of the memory cells includes a floating gate field-effect transistor capable of holding a charge. The data in a cell is determined by the presence or absence of the charge in the floating gate. The cells are usually grouped into sections called “erase blocks”. Each of the cells within an erase block can be electrically programmed in a random basis by charging the floating gate. The charge can be removed from the floating gate by a block erase operation, wherein all floating gate memory cells in the erase block are erased in a single operation.
ICs and memories are designed to operate over a set range of supply voltages and temperatures. In modern ICs and memories the supply voltages have become increasingly smaller, which in part decreases the power usage in these circuits. A number of variations of the band-gap voltage reference circuit are available in the art to compensate the band-gap reference circuit over the ranges of operating temperatures. However, these circuits become less effective at compensation as the supply voltage gets lower. An example of this is in modern Flash memories where the operating voltage is 1.65V and the operating temperature range is −40° C. to 85° C. The situation is even more problematic in portable devices as total power used becomes more of an issue and the band-gap voltage reference circuit must draw as little current as possible (typically no more than 10 μA). Further compounding the issue is the fact that band-gap voltage references typically utilize bipolar junction transistors (BJTs) in their circuits and many of the ICs and memories that they are implemented in do not natively offer high quality BJTs in the underlying integrated circuit technology they are manufactured in.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved compensated band-gap voltage in modern ICs and memory circuits.